Aqueous compositions and their use in the manufacture of paper and paperboard

ABSTRACT

A process of preparing an aqueous composition comprising a polysilicate, wherein the composition is a substantially uniform liquid when measured at 25° C., comprising the steps of, i) providing an aqueous liquid having a source of silicate, ii) adjusting the pH of the liquid to between about 2 and about 10.5, thereby causing polymerisation of the silicate, iii) allowing sufficient time for the polymerisation to proceed to substantial completion and thereby forming a product comprising gelled material, iv) subjecting the gelled material to sufficient shear to form a substantially uniform liquid. The novel aqueous composition made by this process is useful in the manufacture of paper and paperboard either as a mineral filler or as a retention/drainage aid.

The present invention relates to aqueous polysilicate compositions andtheir preparation and use as either mineral fillers, strength aids orretention/drainage aids in the manufacture of paper and paperboard. Alsoincluded in the present invention of processes of making paper andpaperboard in which the aqueous polysilicate compositions are includedas mineral fillers and/or strength aids and/or retention/drainage aids.

It is common practice to include mineral filler in a papermakingprocess. For instance in EP-A-0880618 a processes of making filled paperis described in which cationised precipitated calcium carbonate (PCC) isincluded into a cellulosic suspension and forming a papermaking thinstock containing PCC. The process employs a polymeric retention aidhaving an intrinsic viscosity of at least 4 dl/g and an anionic microparticulate material, such as micro particulate silica material andswellable clay. Filler retention is improved and the process allows theproduction of highly filled paper.

WO-A-99/04092 is concerned with the problems of reduced strength thatcan occur with high filled paper. A process is proposed in which asilicate composition is introduced into a cellulosic suspension and inwhich the silicate forms a three-dimensional network around thecellulosic fibres. In one system (Ca—Flocc) a silicate such as sodiumsilicate is mixed with a calcium compound, such as calcium oxide, themixture is mixed with cellulosic fibre which is then acidified to a pHof between 7 and 9 and polymerisation of the silicate occurs. Anothersystem proposed (Mg—Flocc) uses for instance sodium silicate and amagnesium compound in place of the calcium compound. In this casepolymerisation or gelling of the reaction mixture can be done partlyoutside the presence in the fibre, although the mixture will continue topolymerise in the presence in the fibre. A further system proposed(Si—Flocc) employs silicate which is then acidified to a pH of fromabout 7 to 9. Aluminium compounds may be added to any of the threesystems.

The Mg—Flocc and Si—Flocc systems can be practised by forming thecompositions started outside the presence of fibre. The polysilicatesystems are allowed to cure by allowing sufficient time to formsufficient cross links, but the system is preferably agitated so that itwill not over solidly. The process provides significant strengthimprovements. However, in some cases there can be problems in achievingconsistent formation and this can lead to sporadic loss of strength. Insuch cases the paper may contain significantly more light spots andholes.

Therefore, there is a need to provide an improved process for preparinghighly filled paper which exhibits improved formation and moreconsistently high strength. There is also a need for a process whichprovides paper having further improvements in strength, particularly wetstrength.

It is common practice to use retention and drainage aids in themanufacture of paper and paperboard. For instance cationicpolyacrylamides and cationic starch are very effectiveretention/drainage aids used in papermaking. U.S. Pat. No. 4,388,150describes a binder composition comprising colloidal silica and cationicstarch for addition to the papermaking stock to improve retention of thestock components or for addition to the white water to reduce pollutionproblems and to recover stock components values. The colloidal silicamay take various forms, including that of polysilicic acid, as that thebest results are obtained through the use of silica in colloidal form.Polysilicic acid itself is said to be undesirable and withoutstabilisation deteriorates on storage.

U.S. Pat. No. 4,954,220 discloses work which reveals that some storageor ageing of polysilicic acid is desirable. However, the patent statesthat complete gelation of aqueous solutions of polysilicic acid is to beavoided since once gelled the solutions have little benefits for use asa retention and drainage aid. U.S. Pat. No. 4,954,220 reveals that thestorage or ageing of polysilicic acid that leads to the formation ofsilica micro gels is beneficial and the use of the silica micro gelswith various cationic polymers is said to provide retention and drainageaid systems which are at least the equivalent and in many cases superiorof those provided by colloidal silica/cationic starch combinations. Thesilica micro gels can be formed by acidification of silicate to a pH ofabout 2 to 10.5, some storage or ageing of the solution is usuallyrequired to permit the formation of polysilicic acid micro gels andafter the ageing period, which may be very brief (a few minutes or so)the solution is diluted to about 1 weight % or less in order tostabilise it and retard further growth of the micro gels.

EP-A-0235893 describes a process for making paper and paperboard byadding a cationic polymer of molecular weight of at least 500,000 beforea shear stage and an inorganic material comprising bentonite after thatshear stage. The process has brought about significant benefits in termsof improved drainage time and increased fibre and filler retention.

However, despite these improvements there is still a need for analternative retention/drainage system that provides an equivalent orimproved combination of retention and drainage. In addition it would bedesirable to provide a method of making paper and exhibiting improvedvisual properties and/or strength characteristics, especially in makingfilled paper and in particular where the filler is a synthetic filler.

According to the present invention we provide an aqueous compositioncomprising polysilicate which is particularly useful either as beingmineral filler or as a retention/drainage aid. The aqueous compositionwhen used as a mineral filler allows for formation of highly filledpaper exhibiting high strength and formation. In addition, we have foundthat when the aqueous composition is used at least as part of theretention/drainage system retention and drainage are at least aseffective as known systems using inorganic retention/drainage aids, forinstance micro particulate silica based systems or systems employingswellable clay.

In one aspect of the present invention we provide a process of preparingan aqueous composition comprising a polysilicate, wherein thecomposition is a substantially uniform liquid when measured at 25° C.,comprising the steps of,

i) providing an aqueous liquid having a source of silicate,

ii) adjusting the pH of the liquid to between about 2 and about 10.5,thereby causing polymerisation of the silicate,

iii) allowing sufficient time for the polymerisation to proceed tosubstantial completion and thereby forming a product comprising gelledmaterial,

iv) subjecting the gelled material to sufficient shear to form asubstantially uniform liquid.

The source of silicate may be a suitable silicate compound that willundergo gelation to form a polysilicate. Suitably such silicatecompounds are water-soluble monomeric silicates of monovalent cations.Preferably the source of silicate is selected from the group consistingof sodium silicate, potassium silicate and lithium silicate.

The concentration of silicate is desirably sufficient to provide optimumpolymerisation. If the concentration is too low then polymerisation willnot occur or will proceed at a rate which is unacceptably slow. If theconcentration is too high then the rate of polymerisation is likely tobe uncontrollable. Suitably the concentration of sodium silicate shouldbe in the range that the 1% to about 7%, preferably from about 2% toabout 3%.

It may be desirable to include aluminium compounds in the aqueous liquidof step (i). The presence of aluminium ions will tend to increase therate of gelation and induce the formation of cross links. This may bebeneficial for reducing the reaction time. Typically the aluminiumcompound will be any suitable water-soluble aluminium compound, forinstance aluminium sulphate or alum. Typically an aluminium compound,such as alum, may be added in an amount up to about 0.4 g/g of silicate.Thus in a preferred form a polysilicate is a poly alumino silicate.

The acidification may be achieved by introducing acidic compounds, suchas mineral acids or by introducing substances which dissolve in theaqueous liquid to form acid, such as carbon dioxide. Alternativelyacidification may be achieved using ion exchange resins. Preferablyacidification is achieved by the addition of gaseous carbon dioxide. Theacidification should be to a pH that provides optimum polymerisation orgelation. Desirably in step (ii) the pH is adjusted to between 4 and 9,preferably to between 6 and 8.

The polymerisation of silicate should proceed substantially tocompletion. In this context substantially to completion means that thereis no evident further gelation occurring, although it is possible thatthere is some degree of reaction still occurring to a lesser extent. Inone form polymerisation of an aqueous solution of silicate can beconducted in a vessel to produce a product that is a uniform gelledsolid. However, in this form it may be less convenient to carry out theshearing in the final stage of the process. Therefore, it is usuallypreferred to agitate the liquid during the polymerisation step. Thus ina preferred form the product formed in step (iii) comprises amorphousgelled solids dispersed in the liquid.

The first three steps of this process may be carried out in a similarmanner to that described in WO-A-99/04092, especially in regard to thepreparation of Si—Flocc in absence of cellulosic fibre, given on pages19, 30 and 31. The product formed will contain gelled polysilicate,typically in the form of amorphous solids dispersed in a relatively lowviscosity liquid.

The final step of process may be achieved by using any conventional highshear equipment. Desirably the shearing equipment can be either aSilverson or an Ultra Thurrax Homogeniser. In one preferred form theproduct containing the gelled silicate is subjected to shearing usingeither piece of equipment for one minute at 8000 rpm. The shearing mustbe sufficient to ensure that a substantially uniform liquid is formed.By substantially uniform liquid we mean that the liquid containsessentially no large sized polysilicate solids which are clearlyvisible. By this we mean that there are substantially no particles ofseveral millimetres or more. However, it is possible that thecomposition comprises very small polysilicate particles. Such very smallpolysilicate particles would normally be less than 1 mm in diameter, forinstance and at least 90% by weight below 1 mm diameter. Preferably suchvery small polysilicate particles will be below 750 microns, preferablybelow 500 microns. Generally, any polysilicate particles of particlediameter greater than 150 microns should form less than one-third of theaqueous composition. Preferably the composition will comprise less than20% by weight polysilicate particles of diameter greater than 150microns, more preferably less than 10%. It is especially preferred theproportion of such polysilicate particles will be less than 1% and inparticular less than 0.1%. Furthermore, it is preferred that the aqueouscomposition does not contain any other solids, for instance cellulosicfibres.

The aqueous composition formed by this process is novel. The compositionmust be in form of a uniform liquid. It may for instance be in the formof a uniform gelatinous paste. Typically the composition will besignificantly more viscous than the dispersion of amorphous polysilicatesolids. Preferably an aqueous composition of the invention will exhibita viscosity of at least 200 mPas (when measured at 2% by weightconcentration at 25° C. using a Brookfield viscometer, at 20 rpm,spindle No 2) and preferably at least 300 or 400 mPas and morepreferably at least 600 mPas. It is particularly preferred that theviscosity is at least 1500 mPas (when measured at 2% by weightconcentration at 25° C. using a Brookfield viscometer, at 20 rpm,spindle No 3). The viscosity may be as high as 5000 mPas or higher.Usually though the viscosity will be in the range of between 1700 and3000 mPas, preferably around 2000 mPas.

The polysilicate comprised in the aqueous composition will normally havea relatively high surface area in comparison to many conventionalmineral fillers, such as ground calcium carbonate. However, bycomparison to many micro particulate polysilicate products such aspolysilicate micro gels, the polysilicate will tend to have a relativelylow surface area. Generally the polysilicate has a surface area of below2000 m²/g, preferably in the range of from 750 to 1250 m²/g, morepreferably around 1000 m²/g.

The S-value indicates the degree of aggregation or microgel formationand a lower S-value is indicative of a higher degree of aggregation. TheS-value can be measured and calculated as described by Iler & Dalton inJ. Phys. Chem. 60 (1956), 955-957. Typically a polysilicate micro gelwill exhibit and S-value of around 12% or higher. The polysilicatecomprised in the aqueous composition of the present invention willtypically have an S-value of below 5%. Preferably the polysilicate willhave an S-value in the range of 1 to 4%, preferably around 2.5 to 3.5%.

The aqueous composition according to the present invention is a novelentity and can be defined by the unique combination of parameters. Thuswe provide an aqueous composition comprising a polysilicate, wherein thecomposition is a substantially uniform liquid when measured in at 25° C.and the composition exhibits a viscosity of at least 200 mPas (whenmeasured at 2% by weight concentration at 25° C. using a Brookfieldviscometer, at 20 rpm, spindle No 2) and preferably at least 300 or 400mPas and more preferably at least 600 mPas, and wherein the polysilicatehas a surface area of below 2000 m²/g and has an S-value of below 5%. Itis particularly preferred that the viscosity is at least. It isparticularly preferred that the viscosity is at least 1500 mPas (whenmeasured at 2% by weight concentration at 25° C. using a Brookfieldviscometer, at 20 rpm, spindle No 3). More preferred embodiments may bedefined by the more specific viscosity, surface area and S-valueparameters mentioned above.

The aqueous composition according to the present invention may beprovided in any convenient form. Typically the aqueous composition willcomprise a concentration of SiO₂ which is at least 0.01% by weight,preferably from about 1% to about 45%. More preferably the concentrationwill be between a about 1% and 7%, most preferably between 2% and 3%. Aparticular advantage of the aqueous composition is that it can be addedinto the cellulosic suspension without further modification.

The aqueous polysilicate composition of the invention is particularlysuitable for use in the manufacture of paper or paperboard either as amineral filler a strength aid or as a drainage/retention aid.

The present invention includes a process of making paper or paperboardcomprising forming a cellulosic suspension, draining water from thesuspension to form a wet sheet and then drying the sheet, characterisedin that the aqueous polysilicate composition according to any ofembodiments described herein is added to the cellulosic suspension.

Furthermore, the present invention also concerns a process of makingpaper or paperboard comprising forming a cellulosic suspension, drainingwater from the suspension to form a wet sheet and then drying the sheet,wherein an aqueous polysilicate is added to the cellulosic suspension,in which the aqueous polysilicate is formed by a method comprising thesteps of,

i) providing an aqueous liquid having a source of silicate,

ii) adjusting the pH of the liquid to between about 2 and about 10.5,thereby causing polymerisation of the silicate,

iii) allowing sufficient time for the polymerisation to proceed tosubstantial completion and thereby forming a product comprising gelledmaterial, characterised in that the product of step (iii) is shearedbefore addition to the cellulosic suspension.

We have found that there are particular benefits in applying shear tothe gelled polysilicate material prior to adding this to the cellulosicsuspension. In particular we find that for equivalent filler contentsimprovements in strength can be achieved.

In a further form of the present invention we provide a process ofmaking paper or paperboard comprising forming a cellulosic suspension,mixing a mineral filler into the suspension, draining water from thesuspension to form a wet sheet and then drying the sheet, characterisedin that the mineral filler comprises the aqueous polysilicatecomposition according to any of embodiments described herein.

The process enables highly filled paper to be prepared which exhibitshigh strength and improved formation. In particular the paper that isproduced by this process is consistently of high-quality and exhibits nolight spots or holes.

The aqueous polysilicate composition should be added to the cellulosicsuspension in amounts consistent with those usually used for mineralfillers. Desirably the aqueous composition will be added in an amount offrom 20 to 250 kg per tonne based on dry weight of cellulosicsuspension. The polysilicate of the aqueous suspension may be the onlyfiller used or alternatively further fillers may be used. In the casewhere other fillers are used in addition to the aqueous composition,these fillers may for instance be organic pigments, for the enhancementof paper opacity. Alternatively at least one further mineral filler canbe used additional to the aqueous composition. The further mineralfillers may be any of the conventional fillers and these will includeprecipitated calcium carbonate (PCC), ground calcium carbonate, clay,calcined clay, talc, zeolites, silicas, titanium dioxide and structuredpigments.

The aqueous polysilicate composition and further filler may be combinedprior to addition to the cellulosic suspension. However, it is preferredthat the aqueous composition and the further filler and are addedseparately. In some situations in may be beneficial to add the aqueouscomposition simultaneously with the further filler although usually itwould be expected to add them sequentially. For some papermakingprocesses it may be desired for the aqueous composition and to be addedto the cellulosic suspension prior to the further filler. Generally, itis preferred that the further filler is added first.

In the process of making paper in may also be desirable to include inthe cellulosic suspension a retention and drainage system. This may forinstance be any of the conventional retention and drainage aids that arecommercially available. Preferably the retention and drainage systemwill include a polymeric retention/drainage aid and a micro particulateretention/drainage aid. The polymeric retention/drainage aid can be anyof the group consisting of substantially water-soluble anionic,non-ionic, cationic and amphoteric polymers. The polymers may be naturalpolymers such as starch or guar gums, which can be modified orunmodified. Alternatively the polymers can be synthetic polymers, forinstance polymers prepared by polymerising water-soluble ethylenicallyunsaturated monomers such as acrylamides, acrylic acid, alkali metal orammonium acrylates or quaternised dialkyl amino alkyl-(meth) acrylatesor -(meth) acrylamides. Usually the polymers will have a high molecularweight, for instance at least 500,000. Preferably the polymers will havemolecular weights ranging from at least one million up to 20 or 30million or higher. Typically the polymers will have molecular weightsbetween 5 and 15 million.

The micro particulate retention/drainage aid can be based oncross-linked organic polymers. Typically such polymers may be in theform of micro emulsions, for instance as described in EP484,617 andcommercialised by Ciba Specialty Chemicals under the trade namePolyflex. Alternatively the micro particulate retention/drainage aid maybe inorganic, such as silica microgels, colloidal silica, silica sols,silica gels, polysilicates, aluminosilicates, polyaluminosilicates,borosilicates, polyborosilicates, zeolites or swellable clay.

The swellable clays may for instance be typically a bentonite type clay.The preferred clays are swellable in water and include clays which arenaturally water swellable or clays which can be modified, for instanceby ion exchange to render them water swellable. Suitable water swellableclays include but are not limited to clays often referred to ashectorite, smectites, montmorillonites, nontronites, saponite,sauconite, hormites, attapulgites and sepiolites. Typical anionicswelling clays are described in EP-A-235893 and EP-A-335575.

The aqueous composition may be added as a filler to the cellulosicsuspension as a thin stock, that is after dilution. Alternatively in maybe added further back in the system, for instance in the thick stock,the blend chest or the mixing chest. The point of addition may varyaccording to the particular layout of the paper making machine and thefiller will be added at a point of addition that will give optimumincorporation into the cellulosic medium and optimum retention.Preferably the aqueous composition as a filler will be mixed into thecellulosic suspension before the retention and drainage system.Therefore preferably the retention and drainage system is applied to thecellulosic suspension subsequent to the addition of the mineral filler.

According to a further form of invention, the aqueous compositioncomprising polysilicate forms part or all of the retention and drainagesystem. Thus we have found that the aqueous composition can perform in asimilar manner to existing retention/drainage aids, in particular microparticulate products such as silica sols or swellable clays.

Therefore, according to this aspect of the invention we provide aprocess of making paper or paperboard comprising forming a cellulosicsuspension, applying a retention and drainage system to the suspension,draining water from the suspension form a sheet and then drying thesheet, characterised in that the retention and drainage system comprisesmixing into the cellulosic suspension the aqueous polysilicatecomposition according to any of the embodiments described herein.

When used as a retention/drainage aid the aqueous polysilicatecomposition is desirably mixed into the cellulosic suspension in anamount of at least 100 g per tonne, based on weight of silica on dryweight of suspension. Preferably the amount will be at least 500 gramsper tonne and usually significantly higher, especially when usedsubstantially in the absence of micro particulate retention/drainageaids. We have found that for some systems optimum retention and drainageis achieved using doses as high as 250 kg per tonne. In one preferredform the dose is in the range of 20 to 250 kg per tonne.

The aqueous polysilicate composition will normally form part of theretention and drainage system. Thus in addition to the aqueouscomposition the retention and drainage system preferably furthercomprises mixing into the cellulosic suspension a polymericretention/drainage aid and/or a micro particulate retention/drainageaid. Usually though, the aqueous polysilicate composition is used as apartial or complete replacement of the micro particulateretention/drainage aid and thus will normally be used in a system thatincludes the use of a polymeric retention/drainage aid.

The polymeric retention/drainage aid can be selected from the groupconsisting of substantially water-soluble anionic, non-ionic, cationicand amphoteric polymers. The polymers may be any of the aforementionedpolymeric retention/drainage aids.

The micro particulate retention/drainage aid can be based oncross-linked organic polymers, for instance as described in EP-A484617.Alternatively the micro particulate retention/drainage aid may beinorganic, such as silica microgels, colloidal silica, silica sols,silica gels, polysilicates, aluminosilicates, polyaluminosilicates,borosilicates, polyborosilicates, zeolites or swellable clay. The microparticulate retention/drainage aid may be for instance bentonite typeclays as given in EP-A-235,893, but desirably can be any of those microparticulate materials described above.

In one preferred embodiment of the invention a polymericretention/drainage aid is mixed into the cellulosic suspension before atleast one shear stage. The shear stage can be for instance mixing,cleaning or pumping stages, including for instance fan pumps andcentri-screens etc. A retention/drainage aid comprising the aqueouspolysilicate composition may then be added after that shear stage. Thuspolymeric retention/drainage aid can be added to the cellulosicsuspension followed by one or more shear stages and then the aqueouspolysilicate composition can be added to the cellulosic suspension. Inan alternative system a micro particulate retention/drainage aid is alsoadded to the cellulosic suspension after that shear stage.

In a still further embodiment of the invention we provide a process ofmaking paper or paperboard comprising forming a cellulosic suspension,mixing a mineral filler into the cellulosic suspension, applying aretention and drainage system that the suspension, draining water fromthe suspension to form a wet sheet and drying the sheet, characterisedin that the mineral filler comprises the aqueous polysilicatecomposition of the invention, the suspension is passed through at leastone shear stage before applying the retention and drainage system, andin which the retention and drainage system comprises introducing intothe cellulosic suspension the aqueous polysilicate composition of theinvention and in which the shear stage is selected from mixing, cleaningand pumping stages.

In one preferred form of this embodiment PCC mineral filler is added tothe cellulosic suspension and the suspension is passed through at leastone shear stage. The aqueous polysilicate composition of the inventionis then mixed into the cellulosic suspension as part of the mineralfiller. More preferably once the mineral filler, comprising the aqueouspolysilicate composition, has been added the cellulosic suspension ispassed through at least one shear stage followed by the addition of apolymeric retention/drainage aid. The cellulosic suspension is thenpassed through at least one further shear stage after which aretention/drainage aid comprising the aqueous polysilicate compositionof invention is added to the cellulosic suspension. A micro particulateretention/drainage aid may also be added to the cellulosic suspensionprior to, simultaneously with or after the addition of theretention/drainage aid comprising the aqueous polysilicate composition.

In one illustration of the invention an aqueous polysilicate compositionis made first by preparation of a 2 weight % as SiO₂ amorphous silicagel created by the addition of carbon dioxide to a dilute solution ofwater glass (28.5% soluble silicate 9.2% sodium oxide). A significantquantity (up to possibly over 50%) of the silicate can be replaced witheither sodium decaborate or sodium aluminate or other materials prior tocarbonation. The solution is acidified to a pH of 6.9 to 7.1 and allowedthe gel completely with limited stirring to produce a silica gel slurrycomprising solid gel pieces and a less viscous solution. This gel slurryis sheared using a Silverson at 8000 rpm for one minute to produce asmooth viscous solution.

The smooth viscous polysilicate solution is then added to the papermaking furnish prior to the retention and drainage aid in order toincrease ash content of paper last retaining the paper strength.

EXAMPLES

Preparation of Aqueous Polysilicate Composition (APC) in all Examples

A steady stream of CO₂ was bubbled into a 2 wt % as SiO₂ sodium silicatesolution (Na (3.27) 38/40 F from Akzo PQ Silica). pH was monitored withtime using a calibrated pH electrode.

Preparation of Paper Sheets in all Cases

Five sheets for each variant listed below were prepared using thefollowing order of addition.

Standard additions of 0.5 kgt⁻¹ cationic polyacrylamide (CPAM) and 2.0kg⁻¹ and in bentonite slurry (BentS) were used for all handsheetswithout APC as a retention and drainage aid. Where APC was used as amicroparticle 0.5 kgt⁻¹ cationic polyacrylamide was used as the cationicspecies. Dosages calculated on dry weight of cellulosic suspension(stock). The sequence of treatments is as follows: Stock 5 s PCC 5 s(APC) 5 s CPAM 50 s (BentS) 15 s shear shear shear shear or shear 1000rpm 1000 rpm 1000 rpm 1000 rpm (APC) 500 rpm

Handsheets were prepared after the final mixing step and dried for 2hours at 60° C. on the rotary drier.

Sheet Testing

Sheets were tested for tensile strength using an Instron 4400 at UMISTaccording to Tappi test method. T 494 OM-88.

The paper samples used for strength testing were then used to determinethe total filler content of the handsheets by ashing at 500° C. for 2hours.

Example 1 Preparation of Aqueous Polysilicate Composition (APC)

The preparation of APC was in accordance with the above description. ThepH was monitored and recorded in Table 1. TABLE 1 Time (mins) pH 0 11.05Weight Sodium Silicate (water glass) = 69.97 g 1 10.13 Weight SodiumSilicate + H₂O = 1007.3 g 2 — 3 8.99 4 8.14 5 7.10 6 7.02 7 7.02 Gelledat 7 minutes 8 7.02 9 7.05 10 7.06 15 7.06

Example 2 Effect of Shear on APC Performance

100 mls APC was sheared for the relative time at 20,000 rpm using anUltra Thurrax homogeniser. The results are shown in Table 2. TABLE 2 AshContent Breaking No Variant APC addition Point (%) Length (m) 1 5.0% APC(no shear) 5 secs pre polymer 41.0 1548.9 2 5.0% APC (30 s shear) 5 secspre polymer 39.2 2163.2 3 5.0% APC (60 s shear) 5 secs pre polymer 38.12202.7 4 5.0% APC (15 s shear) 5 secs pre polymer 38.7 2076.7

All sheets contained 35% PCC to target a sheet ash content of 40%.

In the results clearly show that shearing the aqueous polysilicatecomposition improves the paper strength.

Example 3 Effect of Addition Point on APC Performance

Sheared APC was used throughout (1 min at 20000 rpm using an UltraThurrax homogeniser). The results are shown in Table 3. TABLE 3 AshContent Breaking No Variant APC addition Point (%) Length (m) 19 5.0%APC (sheared) 10 mins pre polymer 37.7 2241.0 20 5.0% APC (sheared)  5mins pre polymer 37.9 2258.8 21 5.0% APC (sheared)  1 min pre polymer38.3 2077.1 22 5.0% APC (sheared)  5 secs pre polymer 38.2 2140.5 235.0% APC (sheared) Pre BentS 41.3 1624.9 24 5.0% APC (sheared) PostBentS 40.6 1592.2 25 5.0% APC (sheared) Replace BentS 39.7 2093.

All sheets contained 35% PCC to target a sheet ash content of 40%.

The results show improvements in strength using the sheared aqueouspolysilicate composition, especially when it is added before thepolymer.

Example 4 Preparation of Aluminated APC Samples

Sample Preparation TABLE 4 100% Aluminated APC Time Weight SodiumAluminate = 5.53 g (mins) pH Weight Sodium Silicate = 0.00 g 0 — Weightsolids and water = 200.1 g 0 12.4 (post Al) 1 11.03 After 20 s of CO₂addition a white turbid 2 10.46 precipitate was formed 3 9.38 4 7.5 57.3 7 7.15 9 7.12 11  7.11 13  7.11 15  7.11

TABLE 5 50% Aluminated APC Time Weight Sodium Aluminate = 2.77 g (mins)pH Weight Sodium Silicate = 7.05 g 0 11.10 Weight solids and water =201.3 g 0 12.3 (post Al) 1 10.38 The solution gelled Solid after 2 9.811 minute of CO₂ addition 3 9.47 4 9.07 5 8 7 7.4 9 6.96 11  9.92 13 6.89 15  6.89 Sampled

TABLE 6 10% Aluminated APC Time Weight Sodium Aluminate = 0.553 g (mins)pH Weight Sodium Silicate = 12.21 g 0 11.07 Weight solids and water =200.4 g 0 11.41 (post Al) 1 9.12 No gelling of the carbonated mixturewas observed 2 6.98 during carbonation. After 1 hour standing the sample3 6.83 had gelled 4 6.83 5 6.82 7 6.82 9 6.82 11  6.82 13  6.82 15  8.62Sampled

TABLE 7 5% Aluminated APC Time Weight Sodium Aluminate = 0.277 g (mins)pH Weight Sodium Silicate = 13.26 g 0 11.00 Weight solids and water =200.9 g 0 11.34 (post Al) 1 9.32 No gelling of the carbonated mixturewas observed 2 8.23 during carbonation. After 1 hour standing the sample3 6.87 had gelled as usual 4 6.84 5 6.83 7 6.83 9 6.83 11  6.83 13  6.8315  6.83

TABLE 8 Standard APC Time Weight Sodium Aluminate = 0.0 g (mins) pHWeight Sodium Silicate = 14.00 g 0 10.98 Weight solids and water = 199.6g 1 9.82 2 8.38 Sample gelled at 7 mins 3 6.95 4 6.92 5 6.93 7 6.92 96.92 11 6.92 13 6.92 15 6.92 Sampled

TABLE 9 Average Average Ash Breaking Content Variant APC Addition PointLength (m) (%) 30% PCC N/A 3122.1 30.6 50 kgt⁻¹ standard APC Before R&Dsystem 4412.5 19.0 50 kgt⁻¹ 50% Al APC Replacing BentS 4149.5 23.9 50kgt⁻¹ standard APC Replacing BentS 3886.8 25.2 25% PCC N/A 3868.9 24.450 kgt⁻¹ 10% Al APC Replacing BentS 3903.1 26.0 50 kgt⁻¹ 5% Al APCBefore R&D system 4178.4 21.8 50 kgt⁻¹ standard APC Replacing BentS3964.7 24.2 50 kgt⁻¹ 10% Al APC Before R&D system 4165.9 21.4 50 kgt⁻¹50% Al APC Before R&D system 4392.4 19.9 20% PCC N/A 4115.6 20.6 50kgt⁻¹ 5% Al APC Replacing BentS 3861.4 25.3 50 kgt⁻¹ 100% Al APCReplacing BentS 3436.2 24.2 15% PCC N/A 4839.2 16.0

All APC containing variants contained 20% PCC to target an ash contentof 25% in the finished sheet.

Example 5 Effect of Polyaluminosilicate Microgel (MG) at APC AdditionLevels

TABLE 10 Average Average Ash Breaking Content Variant APC Addition PointLength (m) (%)  5% standard APC Before R&D system 3671.8 23.4  5% MGBefore R&D system 5714.7 6.9 30% PCC N/A 2016.8 33.1 25% PCC N/A 2814.124.7 20% PCC N/A 3104.7 19.6 15% PCC N/A 3794.0 15.2  0% PCC N/A 6412.9.4

All APC containing variants contained 20% PCC to target an ash contentof 25% in the finished sheet.

Example 6

A number of handsheets were prepared with samples of APC sheared tovarious levels using a number of homogenisers and shearing for differentlengths of time.

The sheared samples of APC were assessed for viscosity and lump weightThe prepared sheets were tested for tensile strength, ash content, andfor appearance.

APC Sample Preparation

A 2.0 wt % sample of APC was prepared according to the method outlinedin the first paragraph under examples.

200 mls of the APC sample was sheared for various intervals using eithera Silverson at 2,000 rpm or an Ultra Thurrax homogeniser at 13,500 rpm.TABLE 11 Shear used for APC samples Sample Mixer Time (s) Shear 1 NoShear 0 Shear 2 Ultra Thurrax 13,500 rpm 120 Shear 3 Ultra Thurrax13,500 rpm 15 Shear 4 Silverson 2000 rpm 60 Shear 5 Silverson 2000 rpm30 Shear 6 Silverson 2000 rpm 15

A 1 wt % sample of cationic polyacrylamide (CPAM) and a 5 wt % sample ofbentonites slurry (BentS) were prepared.

A 50:50 blend of hard and softwoods, beaten to 50° SR was prepared anddiluted to a consistency of 0.5% solids.

A 10% slurry of Calopaque F (PCC) was prepared.

The cationic polyacrylamide and the bentonite slurry were diluted to0.1% prior to stock addition.

Handsheet Preparation

5 sets of sheets for each variant listed below were prepared using thefollowing order of addition.

Standard additions of 0.5 kgt⁻¹ cationic polyacrylamide and 2.0 kgt⁻¹bentonite slurry were used for all handsheets.

The following sequence was employed. Stock 5 s PCC 5 s APC 5 s CPAM 50 sBentS 15 s Shear Shear Shear Shear Shear 1000 rpm 1000 rpm 1000 rpm 1000rpm 500 rpm

Handsheets were prepared after the final mixing step, and dried on therotary drier for 2 hours at 65° C. TABLE 13 No Variant 13 20% PCC and 5%APC (Shear 2) 15 20% PCC and 5% APC (Shear 1) 16 20% PCC and 5% APC(Shear 3) 17 20% PCC and 5% APC (Shear 4) 18 20% PCC and 5% APC (Shear5) 19 20% PCC and 5% APC (Shear 6) 26 15% PCC 27 20% PCC 28 25% PCC 2930% PCC 30 35% PCCAPC Evaluation

The samples of sheared (and unsheared APC) were evaluated using aBrookfield viscometer at 20 rpm for low shear viscosity and for lumpweight. Lump weight was determined by taking 100 mis of the APC sample,diluting to 500 mls with tap water and filtering through a pre weighed150μ sieve. The APC was then washed with a further 100 mis of tap waterbefore all excess water was removed from the sieve using a piece of blueroll. The sieve was then weighed again and the weight of APC lumpscalculated.

Handsheet Testing

The dried sheets were then assessed for appearance using a transparencyscanner to give a greyscale impression of the sheet with the gel spotsappearing as light spots in the image.

The handsheets were conditioned at 23° C. and at 50% humidity prior totesting for tensile strength at UMIST.

The ash content of the handsheets was determined was carried out at 500°C. for 2 hours.

Results

Sample Preparation TABLE 14 Standard APC Time (mins) pH Weight SodiumSilicate = 70.05 g 0 10.98 Weight solids and water = 999.6 g 1 9.82 28.38 3 6.95 4 6.92 5 6.93 7 6.92 Sample gelled at 7 mins 9 6.92 11 6.9213 6.92 15 6.92

APC Evaluation TABLE 15 APC low shear Viscosity and Lump Counts Sample 12 3 4 5 6 Shear (speed) No Shear UT (13500) UT (13500) Silv. (2000)Silv. (2000) Silv. (2000) Shear Time (s) 120 15 60 30 15 ViscositySpindle No. 1 2 2 2 2 2 Reading 27.5 32.7 34.5 20.0 24.8 19.5 29.5 32.630.5 19.0 22.6 17.5 31.5 31.0 32.5 20.5 23.0 18.4 31.5 31.9 32.3 20.124.0 16.9 27.5 31.5 19.2 Viscosity (mPas) 147.5 638.8 649.25 395.2 472.0364.0 Lump & Sieve Wt. (g) 141.74 96.548 101.76 113.25 117.67 129.09Sieve Wt. (g) 96.418 96.515 96.730 96.676 96.289 96.298 Lump Wt. (g)45.322 0.033 5.030 16.574 21.381 32.792

Handsheet Testing TABLE 16 Strength and Ash Results Breaking Ash ContentNo Variants Length (m) (%) 13 20% PCC and 5% APC (Shear 2) 4062.6 19.415 20% PCC and 5% APC (Shear 1) 2539.9 31.0 16 20% PCC and 5% APC (Shear3) 3054.9 27.5 17 20% PCC and 5% APC (Shear 4) 3220.6 27.3 18 20% PCCand 5% APC (Shear 5) 2837.5 29.2 19 20% PCC and 5% APC (Shear 6) 2787.829.9 26 15% PCC 4244.1 15.8 27 20% PCC 3613.9 20.9 28 25% PCC 3146.825.4 29 30% PCC 2672.7 30.0 30 35% PCC 2158.6 35.1

The strength results were averaged from two measurements from each of 5sheets. The ash contents were performed on each of the five sheetsseparately.

The sheared polysilicate composition of test 13 according to the presentinvention provided equivalent ash content (denoting filler retained inthe paper sheet) and to test 27 in the absence of the polysilicatecomposition but showed an improvement in strength by over 12%.Furthermore, although the unsheared polysilicate of test 15 showed thehighest ash content for equivalent conditions of PCC and polysilicate,and all of the sheared polysilicates provided an increased strength.

Graphical representations of Table 16 can be found in FIGS. 1, and 2.

The Impact of Shear on APC

From the results in Table 15 the weight of APC lumps remaining in thesieve appear to be inversely proportional to the degree of shearapplied. During the viscosity measurements the Brookfield readingdecreased significantly as the testing interval increased. (All theresults were taken after three revolutions of the spindle at 20 rpm)

Effect of Sheared APC on Sheet Strength

The level of shear was optimised for this system in terms of strength.The greatest increase was seen in FIG. 2 corresponding to APC beingsheared for 1 minute at 2000 rpm using the Silverson. The loss ofstrength at lower levels of shear could be explained by thenon-homogenous nature of the silica slurry allowing the silica to remainin discrete particles and to bind to its self rather than to the fibresand fillers.

Effect of Sheared APC on Sheet Appearance

Even a low level of shear removes the appearance of prominent gel spots.The higher level of shear applied to the silica the smaller the gelspots. The sheets were acceptable for all levels of shear applied.

The appearance of the sheet can be improved by eliminating gel spotscaused by unsheared APC.

1. A process of preparing an aqueous composition comprising apolysilicate, wherein the composition is a substantially uniform liquidwhen measured at 25° C., comprising the steps of, i) providing anaqueous liquid having a source of silicate, ii) adjusting the pH of theliquid to between about 2 and about 10.5, thereby causing polymerisationof the silicate, iii) allowing sufficient time for the polymerisation toproceed to substantial completion and thereby forming a productcomprising gelled material, iv) subjecting the gelled material tosufficient shear to form a substantially uniform liquid.
 2. A processaccording to claim 1 in which the source of silicate is selected fromthe group consisting of sodium silicate, potassium silicate and lithiumsilicate.
 3. A process according to claim 1 in which the aqueous liquidin step (i) also comprises aluminium compounds.
 4. A process accordingto claim 1 in which in step (ii) the pH is adjusted to between 4 and 9.5. A process according to claim 1 in which the liquid is subjected toagitation in step (iii).
 6. A process according to claim 1 in which theproduct formed in step (iii) comprises amorphous gelled solids dispersedin a liquid.
 7. An aqueous composition comprising a polysilicateobtainable by a process according to claim
 1. 8. An aqueous compositionaccording to claim 7 which exhibits a viscosity of at least 200 mPas(when measured at 2% by weight concentration at 25° C. using aBrookfield viscometer, at 20 rpm, spindle No 2).
 9. An aqueouscomposition according to claim 7 which exhibits a viscosity of at least1500 mPas (when measured at 2% by weight concentration at 25° C. using aBrookfield viscometer, at 20 rpm, spindle No 3).
 10. An aqueouscomposition according to claim 7, in which the polysilicate has asurface area of below 2000 m²/g.
 11. An aqueous composition according toclaim 7, in which the polysilicate has an S-value of below 5%.
 12. Anaqueous composition comprising a polysilicate, wherein the compositionis a substantially uniform liquid when measured in at 25° C. and thecomposition exhibits a viscosity of at least 200 mPas (when measured at2% by weight concentration at 25° C. using a Brookfield viscometer, at20 rpm, spindle No 2), and wherein the polysilicate has a surface areaof below 2000 m²/g and has an S-value of below 5%.
 13. An aqueouscomposition according to claim 12 which exhibits a viscosity of at least1500 mPas (when measured at 2% by weight concentration at 25° C. using aBrookfield viscometer, at 20 rpm, spindle No 3).
 14. An aqueouscomposition according to claim 7, in which the polysilicate has asurface area of between 750 and 1250 m²/g.
 15. An aqueous compositionaccording to claim 7, in which the polysilicate is apolyaluminosilicate.
 16. An aqueous composition according to claim 7,and in which the concentration Of SiO₂ is at least 0.01% by weight.17-19. (canceled)
 20. A process of making paper or paperboard comprisingforming a cellulosic suspension, draining water from the suspension toform a wet sheet and then drying the sheet, characterised in that theaqueous composition according to claim 7 is added to the cellulosicsuspension.
 21. A process according to claim 20, in which mineral filleris mixed into the cellulosic suspension wherein the mineral fillercomprises the aqueous composition according to claim
 7. 22. A processaccording to claim 21, in which the aqueous composition is added to thecellulosic suspension in an amount of from 20 to 250 kg/tonne based ondry weight of polysilicate and dry weight of cellulosic suspension. 23.A process according to claim 22, in which at least one further filler ismixed with the cellulosic suspension, in which the filler is either amineral filler and/or an organic pigment.
 24. A process according toclaim 23 in which the further filler is selected from the groupconsisting of precipitated calcium carbonate (PCC), ground calciumcarbonate, clays, calcined clays, talc, zeolites, silicas, titaniumdioxide and structured pigments.
 25. A process according to claim 23 inwhich the aqueous composition and the further filler is combined priorto addition to the cellulosic suspension.
 26. A process according toclaim 23 in which the aqueous composition and the further filler areadded separately to the cellulosic suspension.
 27. A process accordingto claim 26 in which the aqueous composition and further filler areadded sequentially to the cellulosic suspension.
 28. A process accordingto claim 18, in which a retention and drainage system is applied to thecellulosic suspension.
 29. A process according to claim 28, in which theretention and drainage system comprises mixing into the cellulosicsuspension a polymeric retention/drainage aid and a micro particulateretention/drainage aid.
 30. A process according to claim 29, in whichthe polymeric retention/drainage aid is selected from the groupconsisting of substantially water-soluble anionic, non-ionic, cationicand amphoteric polymers.
 31. A process according to claim 29, in whichthe micro particulate retention/drainage aid is selected from the groupconsisting of cross linked organic polymers, silica microgels, colloidalsilica, silica sols, silica gels, polysilicates, aluminosilicates,polyaluminosilicates, borosilicates, polyborosilicates, zeolites andswellable clay.
 32. A process according to claim 28, in which theretention and drainage system is applied to the cellulosic suspensionsubsequent to the addition of the mineral filler.
 33. A process ofmaking paper or paperboard comprising forming a cellulosic suspension,applying a retention and drainage system to the suspension, drainingwater from the suspension form a sheet and then drying the sheet,characterised in that the retention and drainage system comprises mixinginto the cellulosic suspension the aqueous composition according toclaim
 7. 34. A process according to claim 33, in which the aqueouscomposition is mixed into the cellulosic suspension in an amount of atleast 100 g/tonne, based on weight of silica on dry weight of cellulosicsuspension.
 35. A process according to claim 33, in which the retentionand drainage system further comprises mixing into the cellulosicsuspension a polymeric retention/drainage aid and/or a micro particulateretention/drainage aid.
 36. A process according to claim 35, in whichpolymeric retention/drainage aid is selected from the group consistingof substantially water-soluble anionic, non-ionic, cationic andamphoteric polymers.
 37. A process according to claim 35, in which themicro particulate retention/drainage aid in selected from the groupconsisting of cross linked organic polymers, silica microgels, colloidalsilica, silica sols, silica gels, polysilicates, aluminosilicates,polyaluminosilicates, borosilicates, polyborosilicates, zeolites orswellable clay.
 38. A process according to claim 33, in which apolymeric retention/drainage aid is mixed into the cellulosic suspensionbefore at least one shear stage selected from mixing, cleaning andpumping stages and then adding to the cellulosic suspension after thatshear stage a retention/drainage aid comprising the aqueous composition.39. A process according to claim 38 in which a micro particulateretention/drainage aid is also added to the cellulosic suspension afterthat shear stage.
 40. A process of making paper or paperboard comprisingforming a cellulosic suspension, mixing mineral filler into thecellulosic suspension, applying a retention and drainage system that thesuspension, draining water from the suspension to form a wet sheet anddrying the sheet, characterised in that the mineral filler comprises theaqueous composition according to claim 7, the suspension is passedthrough at least one shear stage before applying the retention anddrainage system, and in which the retention and drainage systemcomprises introducing into the cellulosic suspension the aqueouscomposition according to claim 7 and in which the shear stage isselected from mixing, cleaning and pumping stages.
 41. A processaccording to claim 40, in which at least one further filler is mixedwith the cellulosic suspension, in which the filler is either a mineralfiller and/or an organic pigment.
 42. A process according to claim 41 inwhich the further filler is selected from the group consisting ofprecipitated calcium carbonate (PCC), ground calcium carbonate, clays,calcined clays, talc, zeolites, silicas, titanium dioxide and structuredpigments.
 43. A process according to claim 41 in which the aqueouscomposition and the further filler is combined prior to addition to thecellulosic suspension.
 44. A process according to claim 40 in which theaqueous composition and the further filler are added separately to thecellulosic suspension.
 45. A process according to claim 44 in which theaqueous composition and further filler are added sequentially to thecellulosic suspension.
 46. A process of making paper or paperboardcomprising forming a cellulosic suspension, mixing mineral filler intothe cellulosic suspension, applying a retention and drainage system thatthe suspension, draining water from the suspension to form a wet sheetand drying the sheet, characterised in that the mineral filler comprisesthe aqueous composition according to claim 7, the suspension is passedthrough at least one shear stage before applying the retention anddrainage system, and in which the retention and drainage systemcomprises introducing into the cellulosic suspension the aqueouscomposition according to claim 7 and in which the shear stage isselected from mixing, cleaning and pumping stages in which PCC mineralfiller is added to the cellulosic suspension and the suspension ispassed through at least one shear stage and then the aqueous compositionaccording to claim 7 is mixed into the cellulosic suspension.
 47. Aprocess of making paper or paperboard comprising forming a cellulosicsuspension, mixing mineral filler into the cellulosic suspension,applying a retention and drainage system that the suspension, drainingwater from the suspension to form a wet sheet and drying the sheet,characterised in that the mineral filler comprises the aqueouscomposition according to claim 7, the suspension is passed through atleast one shear stage before applying the retention and drainage system,and in which the retention and drainage system comprises introducinginto the cellulosic suspension the aqueous composition according toclaim 7 and in which the shear stage is selected from mixing, cleaningand pumping stages, in which subsequent to the addition of mineralfiller comprising the aqueous composition according to claim 7, thecellulosic suspension is passed through at least one shear stagefollowed by the addition of a polymeric retention/drainage aid and thenthe cellulosic suspension is passed through at least one further shearstage after which a retention/drainage aid comprising the compositionaccording to claim 7 is added to the cellulosic suspension.
 48. Aprocess according to claim 47 in which a further micro particulateretention/drainage aid is added to the cellulosic suspension prior to,simultaneously with or after the addition of the retention/drainage aidcomprising the aqueous composition.
 49. A process of making paper orpaperboard comprising forming a cellulosic suspension, adding a strengthaid to the cellulosic suspension, draining water from the suspension toform a wet sheet and drying the sheet, characterised in that thestrength aid comprises the aqueous composition according to claim
 7. 50.A process of making paper or paperboard comprising forming a cellulosicsuspension, draining water from the suspension to form a wet sheet andthen drying the sheet, wherein an aqueous polysilicate is added to thecellulosic suspension, in which the aqueous polysilicate is formed by amethod comprising the steps of, i) providing an aqueous liquid having asource of silicate, ii) adjusting the pH of the liquid to between about2 and about 10.5, thereby causing polymerisation of the silicate, iii)allowing sufficient time for the polymerisation to proceed tosubstantial completion and thereby forming a product comprising gelledmaterial, characterised in that the product of step (iii) is shearedbefore addition to the cellulosic suspension.